Casting steel ingots



Jan. 28, 1941.

CASTING STEEL INGOTS Filed Sept. 7, 1959 FIG. 1.

. 1 f fi 5; W A $2. W u u W 3 w WW? 5 9 E 7w F v K p v. MQ e Patented Jan. 28, 1941 UNITED STATES CASTING STEEL INGOTS Frank T. Bumbaugh and Charles B. Francis, Pittsburgh, Pa.

Application September 7, 1939, Serial No. 293,824

8 Claims.

This invention relates to the casting of steel ingots and particularly to the casting of ingots of steel to which had been added volatile elements or compounds that are poisonous or in- 5 jurious to the health of the workmen. More specifically, we refer to the elements selenium and particularly the element lead which is always added to the steel as it is being teemed into the ingot mold, addition of lead in this way imparting improved machining properties to the steel.

While lead has been added to steel in various forms, it is the more common commercial practice to add the lead, during casting, in the form of fine shot or coarse powder through a chute inclined and supported in a position so that a small stream of solid particles drops into the mold near to the stream of molten metal pouring into the mold. By this procedure the addition of the lead is begun after the pouring has begun and when the ingot mold has been partially filled with molten metal, the depth of metal when the addition of lead is begun varying from one-fourth to one-third the total depth of the mold.

' During the addition of the lead in the manner described, a certain proportion, varying from 40 per cent to 60 per cent, is volatilized, the fusion point of lead being about 2730 degrees Fahrenheit or 100 degrees to 300 degrees Fahrenheit below the liquidus temperature of the various steels to which it is addedl Lead thus volatilized, of course, escapes from the mold to injuriously contaminate the air, for it is well known lead fumes are poisonous to the human system. The probable limit that can be inhaled without serious 35 hazard to the health of the average person is about 0.15 Mg estimated metallic lead per cubic meter of inhaled air.

As the lead fume escapes from the ingot mold and comes in contact with the air, it probably 40 unites with the oxygen in the latter to form one of the oxides of lead, probably lead monoxide,

PbO. However, lead either in elemental form or combined with oxygen .or other elements is equally toxic when inhaled; as a matter of fact, lead taken into the human system in this manner is most effective in producing injurious physiological effects. Other elements added to steel, such as selenium, are similarly volatilized, but .selenium is oxidized to SeO: which is a gas at elevated atmospherictemperatures and requires different treatment than lead.

To protect the workmen and also the steel workscommunity, the fumes that escape from the ingots while they are being cast are drawn away by a suction system into suitable apparatus for their removal by known means. However. after the ingots have been poured, they continue to emit fumes, and it is the object of our invention to prevent the fumes thus emitted by the ingot after casting, 'from contaminating the air. Close observation shows that the fumes given off by the ingot after it has been cast come mainly from the top of the ingot and from the air gap between the ingot wall and the mold wall, which gap forms a few minutes after casting has been completed. As the ingots ordinarily have to be moved away from the suction apparatus shortly after they have been cast, it is an advantage to have some means of preventing the escape of the fumes to the air. Without such means it is necessary to have a suction apparatus located before the top of each ingot and to maintain a high suction in the system of ducts leading from all the ingots of a heat until the ingots have cooled to a temperature at which no further fumes are given off. As this temperature is about 1500 degrees Fahrenheit, the ingots must be held before the suction apparatus for considerable periods of time, varying from thirty minutes to an hour.

To accomplish our purpose we employ a chem ically treated covering to be applied to the top of the ingot as soon as the pouring has ceased. The object of this covering is to provide a kind of filter through which the fumes must pass, which filter will have a cooling effect on the gases passing through it and react chemically with the lead fume toform a less volatile compound than lead oxide. For this purpose we prefer to use a cellulosic substance, such as wood shavings, sawdust or cotton, water and either sulphuric acid or ferrous sulphate. This cellulosic substance is preferably impregnated with sulphuric acid or ferrous sulphate solutions, slightly dried if necessary, then treated with some adhesive substance and pressed into the form of mats having dimensions and a shape corresponding to the tops of the molds on which they are to be used as described later. A porous mineral substance such as loam or granulated blast furnace slag impregnated with sulphuric acid or ferrous sulphate may be substituted for the cellulosic substance. If mineral matter is used, it should be selected for properties to meet the following rer d into the surface in the subsequent rolling operations. Low fusing substances drain off the ingot in the soaking pits.

3. It should have good absorbing capacity for water and particularly solutions of sulphuric acid and ferrous sulphate.

Under some conditions we obtain best results by employing both classes of filters as described below.

In the accompanying drawing, Figure 1 is a section of a mold with which the invention is being used; Figure 2 is a similar showing but the mold is of the bottle-neck type; Figure 2 is the same as Figure 2 except that a cap is used; and Figures 3 and 3 show the mold of Figure 1 using a hot top.

Referring to the drawing, Figure 1 represents an ingot mold that has been filled with liquid steel emitting fumes and closed at the top by an application of our invention. In this drawing the numeral i represents the mold, the numeral 2' a thick pad of the cellulosic substance, and the numeral 3 the impregnated loam or slag. After the mold has been filled withv the liquid steel, a mat of the cellulosic material is placed upon the liquid surface and a quantity of the impregnated mineral material is shoveled on top of the mat. The water contained in the mat and mineral covering, having a high heat of vaporization, has the effect of cooling the fumes when they pass into the filter, causing a condensation into coarser particles that remain trapped in the filter. Chemical action between the lead fume and the sulphate ion, S04, assists in this process of condensation. The covering also has a cooling effect on the top of the steel so that the steel in contact with the filter is cooled below the volatilization point of the lead before the filter itself becomes heated to about 1980 degrees Fahrenheit, the temperature at which lead sulphate itself undergoes decomposition to permit volatilization of the lead.

Because of the different types of ingot molds and other equipment, and also because of the different methods of pouring, various modifications must be made in the method of application of our invention. Figure 2 illustrates one of these modifications to accommodate ourinvention to casting in molds with restricted openings, such as the bottle-neck mold 4. In casting an ingot in a mold of this form, a mat sufficiently large to cover the entire surface of the steel cannot be passed through the top of the mold, and we therefore employ the impregnated mineral filtering medium instead. After the steel has been poured to the proper height, the loam or blast furnace slag or impregnated mineral substance is shoveled into the top of the mold to a depth of four. to five inches as illustrated at 5 in this Figure 2.

Figure 2 shows a bottle-neck mold 6 on which a metal cap 6 is employed regularly to bring about rapid solidification of the steel at the top of the ingot. In applying our invention to this type of mold, the ingot mold is poured full of the metal and the ingot metal cap is placed on top in the usual manner. The moist impregnated filtering medium is shoveled about the openings in the cap in the mold as illustrated and indicated by the numeral 1, forcing the vapors to pa through the wet but porous mass.

. Figures 3 and 3 illustrate the manner of application of our invention to the type of molds known as hot top molds. A-mold of this type has a refractory mineral or metal form 8 which is inserted in the top of the ingot mold 9. In this type of mold it is customary to fill the ingot mold to the bottom of the hot top and after a period sufficient to permit the steel to solidify next to the wall of the ingot, to add more metal, filling the hot top with liquid steel which may descend to fill the pipe cavities formed as the lower portion of the ingot solidifies.

In applying our invention to this method of casting ingots, we fill the mold with steel to the bottom ofthe hot top, adding lead as described at the beginning. Then we add a mat I0 of this cellulosic material which is so shaped as to fit neatly within the hot top. If sufficiently thick, this mat prevents the escape of fumes but does not rapidly solidify the steel at the surface;

neither does the mat burn, because the air is excluded from the surface in contact with the hot steel. To prevent escape of fumes from the air gap between the mold and the steel ingot, we fill the space between the mold and the hot top with the granulated mineral substance that has been impregnated with a solution of sulphuric acid or ferrous sulphate, as illustrated by the numeral I After the steel next to the mold has had time to solidify to the hot top, we fill the hot top as usual by pouring a stream of liquid steel through the cellulosic mat, the hot stream of metal quickly burning a hole through the mat. When the hot top has thus been filled with the liquid steel to the usual depth, we then add the granular mineral substance I2 to form a layer sufficiently thick to filter out the escaping lead fumes. Figure 3 shows the hot top at this last stage.

Zinc, sodium and other basic or amphoteric elementsthat are volatile at liquid steel temperatures may be prevented from contaminating the air in the manner as described above for lead, using the same chemical reagents and the same procedure. To efliciently absorb fumes from acid elements such as sulphur, selenium and tellurium, we proceed in the same manner, using the same cellulosic and mineral substances for the filtering media, but instead of acids, we impregnate the cellulosic or mineral substance with basic compounds. For this purpose we have found magnesia, calcium hydroxide, slaked lime, sodium hydroxide or sodium carbonate satisfactory and the cheapest to use under most conditions. If the cellulosic material is wood, this substance may contain a sufficient amount of alkalies to react with the acid fumes, particularly if a thick, heavy mat is used. Similarly, the organic acids distilled from the wood may be sufficient to react with and retain fumes of a basic character.

'Having thus disclosed certain applications of our invention, we desired it to be understood that this description is not intended to limit the application of our invention, because it may be modified and adapted for use in various ways not mentioned in this disclosure. The novel and useful features of our invention for which we seek Letters Patent are more fully described and defined by the following claims.

We claim:

1. A method of preventing contamination of the air by noxious fumes escaping from an ingot treated with lead, the method being characterized by placing porous material moistened with an .acid solution on too of the ingot while it is still molten.

2. A method of preventing contamination of the air by noxious fumes escaping from an ingot treated with lead, the method being characterized by placing porous material moistened with an acid solution on top of the ingot while it is still molten. the material being in the form of a ,mineral matter having a melting temperature not exceeding about 2000 degrees Fahrenheit.

4. A method of preventing contamination of the air by noxious fumes escaping from an ingot treated with lead, the method being characterized by placing porous material moistened withan acid solution on top of the ingot while it is still molten, the material being sufllciently thick and moistened to a sumcient degree to condense at least some of the fumes or their products resulting from chemical reaction with the acid solution.

5. A steel casting method including casting molten steel in an ingot mold, adding selenium,

are volatilized by the heat of said steel so as to escape from said mold as noxious fumes, applying porous material over said steel in said mold so said mines pass through said material to escape from said mold, and molstening said material, said material having a. melting temperature less than that of said steel.

7. A steel casting method including casting molten steel in an ingot mold, adding selenium, lead or similar substances to said steel at any time while it is molten and which substances are volatilized by the heat of said steel so as to escape from said mold as noxious fumes, applying porous material over said steel in said mold so said fumes pass through said material to escape from said mold, and moistening said material, said material being applied to a thickness and sumclently moistened to effect condensation in said material of said fumes.

8. A steel casting method including casting molten steel in an ingot mold, adding selenium, lead or similar substances to said steel at any time .while it is molten and which substances are volatilized by the heat of said steel so as to escape from said mold as noxious fumes, apply- ;ing porous material over said steel in said mold 

